Isolation of the lactose permease protein is a necessary prerequisite to the study of its structure and function. This integral membrane protein is the product of the y gene, one of three structural genes in the lactose operon of Escherichia coli. Purification and characterization of the permease, followed by determination of its amino acid sequence, will allow a search for sequence homologies within the lac operon to provide insight into operon evolution. The lactose permease is also representative of the large class of transport proteins that require an energized membrane state in order to function. Reconstitution experiments, using the purified protein, will be aimed at analyzing the mechanism of coupling of transport to energy metabolism. Permease isolated from y gene mutant strains will be used to correlate changes in functional properties with specific structural alterations.